1. Field of the Invention
The present invention relates to an optical disk device, and in particular, to a device for writing data onto an optical disk having an emboss section (or a header section) and a data section.
2. Description of the Related Art
In many recordable optical disks, such as the DVD-RAM disk shown in FIGS. 6A and 6B, each sector 104 comprises a header section (emboss section) 104a and a data section 104b. In the emboss section 104a, address information of the sector is formed. The address information is generally constructed from 4 address data. Because these 4 address data are identical, the address information of the sector can be obtained as long as any one of address datum among the four data can be replayed. When replaying, first, a beam of focused laser light (a laser beam) is set at a replaying power to replay the emboss section 104a to obtain the address information, and then the data section 104b is replayed and a replay RF signal is demodulated. When writing, first, the emboss section 104 is replayed at the replaying power to obtain the address information, and then the power of the laser beam is increased to the writing power and data are written onto the data section 104b. 
However, because the emboss section and data section have disk characteristics that are physically different from each other, the optimal control parameters for the cases when the emboss section is replayed and when the data section is replayed or written are different. For example, an optimal focus offset for the emboss section and an optimal focus offset for the data section are different.
In light of this situation, Japanese Patent Laid-Open Publication No. 2000-251273, for example, discloses switching of the control parameters during the seek process for an optical disk. More specifically, this reference discloses that parameters for emboss are used when the emboss section 104a is replayed and the parameters are switched to those for data when the data section 104b is replayed.
However, considering the response characteristics of focus actuators, it is difficult to instantaneously (discontinuously) change the focus position at the boundary between the emboss section 104a and the data section 104b, and, in reality, the focus position is set at the desired position after the laser beam has already proceeded some distance into the data section 104b. Thus, it has been difficult to reliably replay the data section 104b or to reliably write data onto the data section 104b. 
During replay, both emboss section 104a and the data section 104b are replayed at the replaying power, and, thus, the difference in the focus offset is relatively small. However, during writing in which the emboss section 104a is replayed at the replaying power and data are written onto the data section 104b at a writing power, the optimal focus position for the emboss section 104a significantly differs from the optimal focus position for the data section 104b. As a result, it is not possible to rapidly change the focus position at the boundary between the emboss section 104a and the data section 104b. In such a case, if the focus position is fixed at the optimal writing focus position and the emboss section 104a is replayed, the address information may not be obtained, or, even when obtained locally, the address information cannot be constantly obtained over the entire regions of the optical disk 100, and, thus, data cannot be written consistently. On the other hand, when the data are written onto the data section 104b at the optimal replaying focus position, there is a problem in that the writing quality may be degraded, such as, for example, increase in jitter.